Have no fear you can recover the key using a handy utility that reads it from the registry.

This is a life saver for reinstalls on systems where the stickers just not there or the installation disks are missing (along with the key) .

What you do is before wiping the system run this little program, it’ll tell you the licence key, you write it down, then wipe the system reinstall windows using the key you got from the original install. No problems reactivating windows as the key was previously used on that computer.